This invention relates to classification, i.e., removal of fine particles from coarser particles in gas streams. Frequently it is desirable to separate very fine particles (e.g., less than 5 microns) from coarser particles. In one typical application, epoxy coating, heated parts are passed through a fluidized bed of ground epoxy particles. This bed of particles should contain no very fine particles, hence the need for classification.
Two approaches are known in the field, rotating classifiers and cyclone classifiers. Rotating classifiers are subject to high power consumption, high noise generation, and unbalance susceptibility. Cyclone classifiers avoid these drawbacks, yet have been ineffective in removing very fine particles.
In a typical cyclone classifier, one stream of air, containing particles, circulates and swirls around inside a cylindrical housing. Inertial, or centrifugal, forces tend to move the particles toward the outer wall of the housing. A second stream of air, flowing perpendicularly to the first, is intended to entrain and remove the fine particles while leaving the coarse particles behind. In general, these cyclones achieve adequate removal of some fine particles (e.g., 5-10 microns in length) but are inefficient at removing very fine particles (e.g. less than 5 microns).